The present invention relates to an anti-collision system and, more particularly, to an automatic system for enhancing the conspicuousness of an aircraft to the crew of second aircraft posing a collision threat.
The primary mechanism of midair aircraft collision avoidance is a flight crew's application of the "see and avoid" principle. This principle is sufficiently significant to be codified in regulations related to flight operations. For example, U.S. Federal Aviation Administration (FAA) regulation, 14 C.F.R. .sctn.91.113, requires "when weather conditions permit, regardless of whether operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft."
The conspicuousness of an aircraft intruding on the airspace of another aircraft is significant to the timeliness of visual acquisition of the intruder by the crew of the other aircraft. Aircraft are equipped with external recognition lights to enhance their conspicuousness to other air traffic. Recognition lights include a position light system, including red and green forward lights indicating the right and left sides of the plane and a rear mounted white light. FAA regulations also require an anti-collision light system comprising sufficient numbers of flashing lights arranged to illuminate the vital areas around the airplane, considering its physical configuration and flight characteristics. The anti-collision light system must cover a field extending 75 degrees above and below the horizontal plane of the aircraft.
Despite the required external recognition lights and the attention given to the "see and avoid" principle, studies have shown that the primary cause of midair collisions is the failure of a pilot to see another aircraft that poses a threat of collision. Therefore, since the early 1990's, U.S. federal regulations have required that aircraft be equipped with a Traffic Alert and Collision Avoidance System (TCAS) (also known as Airborne Collision Avoidance System (ACAS)) to supplement the "see and avoid" principle. TCAS is an airborne radio system that locates and tracks the progress of aircraft equipped with beacon transponders. A TCAS transmitter in a first, tracking aircraft interrogates transponders of potentially intruding aircraft within range of the system (usually up to about 40 miles). Responding signals or replies from the transponders of aircraft in range are received through a directional antenna by a receiver in the tracking aircraft. The identification and altitude of the intruder are obtained from the replies and the distance and heading of the intruder is calculated and tracked by a TCAS computer in the tracking aircraft. The relative positions of intruders tracked by the TCAS computer are displayed in the tracking aircraft's cockpit.
If the TCAS computer calculates that an intruder is within approximately 35-40 seconds of a potential collision, the system will issue a traffic advisory (TA) indicating to the crew of the tracking aircraft that the intruder is a potential threat. The crew must visually locate the threat and may maneuver vertically with the assistance of air traffic control to resolve the threat. If the aircraft is equipped with a TCAS I system, advisories are limited to traffic advisories. If the tracking aircraft is equipped with a more comprehensive TCAS II system, the traffic advisory will be followed by an resolution advisory (RA) if the intruder approaches within approximately 20-30 seconds of a collision. The TCAS II system can determine whether the intruder is climbing, diving, or in level flight and will advise the pilots of the two aircraft of evasive vertical maneuvers to resolve the course conflict. Even with the TCAS system, the ability to quickly visually locate an intruder is important to avoiding midair collision hazards.
In addition to the position and anti-collision light systems, aircraft are equipped with taxi and landing lights used to illuminate the runway during take-off and landing. The bright landing lights may be used to increase the conspicuousness of an aircraft. For example, a voluntary FAA safety program, "Operation Lights On," recommends turning landing lights on during takeoff and when operating below 10,000 feet, day or night, especially within 10 miles of an airport or under conditions of reduced visibility. Aircraft may also include other external lights such as de-icing lights, strobe lamps, and rudder illumination that can be manually activated to increase conspicuousness and enhance visual acquisition of the aircraft. Switching combinations of these additional lights "on" and "off" can further improve the conspicuousness of the aircraft. Lighting controllers are available that automatically switch individual lights or lighting systems "on" and "off" when activated by the pilot. However, manual light activation can be unreliable, particularly when the aircrew busy searching for approaching traffic.
Campanella, U.S. Pat. No. 3,652,981, discloses a proximity warning system based on detection of an exterior flash lamp or strobe by an electro-optical sensor of a tracking aircraft. The output of the electro-optical sensor is displayed in the cockpit to warn of threatening traffic. In addition, an aural tone may sound to draw the pilot's attention to the situation. In one embodiment, the flash lamp is of an intruding aircraft can triggered by a signal from an airborne weather radar of the tracking aircraft. Once triggered, the flash of the lamp of the intruding aircraft is detected by the electro-optical sensor of the tracking aircraft to produce a warning. While the electro-optical sensor may be able to distinguish between the flash lamp of the proximity warning system and the flashing lamps of the anti-collision warning system on the basis of flash rate, an additional flashing lamp may not significantly enhance the conspicuousness of the aircraft to human observers and the conspicuousness of the tracking aircraft is unchanged by the system. The activation of the flashing light requires that the tracking aircraft be equipped with weather radar and that the potential intruder be equipped an additional radio receiver to detect scanning by the radar of the tracking aircraft. Further, the use of weather radar as part of a reliable proximity warning system is precluded by the limited geometry of the radar beam.
What is desired, therefore, is system that in response to detection of a potential collision threat automatically activates external lighting of an aircraft to enhance its conspicuousness.